Protective system



Feb. 21, 1939. L. F. HUNT 2,147,841

PROTECTIVE SYSTEM im @J/mf@ Feb. 21, 1939. L- F- HUNT 2,147,841

PROTECTIVE SYSTEM Filed Nov. SO, 1936 5 Sheets-Sheet 2 Feb. 21, 1939. L, F. HLINT 2,147,841

PROTECTIVE SYSTEM AML n 7.? 26 9 j MN WWMZ? f M l F. HUNT Feb. 21, 1939.

PROTECTI VE S YS TEM Filed Nov. 30, 1936 5 Sheets-Sheet 4 Bowl m Feb. 21, 1939. F. HUNT 2,147,841

PROTECTIVE SYSTEM Filed Nov. 30, 1936 5 Sheets-Sheet 5 Patented Feb. 21, 1939 UNITED STATES PATENT FFICE 7 Claims.

This invention relates to an electrical protective system and relates more particularly to a protective system for an electrical distributing system. A general object of this invention is to provide an electrical protective system of the character referred to that is highly sensitive to faults in the distributing system and that is very rapid in operation.

Another object of the invention vis to provide improvements in a protective system of the general character described in United States Letters Patent No. 2,051,378, issued August 18, 1936.

The present invention is concerned primarily with a system for protecting a power transmission system and the equipment connected therein against fault conditions. Electrical distribution systems of the character referred to may be effectively protected against phase to phase faults by protective equipment of the general type set forth in United States Letters Patent No. 1,940,303 and No. 1,965,896, but considerable difficulty has been encountered in protecting the distribution systems against phase to ground faults. The protective system described and claimed in the above mentioned Patent No. 2,051,378 has proven quite effective in handling phase to ground faults, but difliculty was experienced in coordinating the power directional relays, the overcurrent relays, and the tripping relays to assure the proper operation of the tripping relays. Further, it was found necessary to employ delayed trip relays which, of course, delayed the opening of the circuit breaker.

Another object of this invention is to provide a protective system of the character mentioned in which the elements are so coordinated that there is no possibility of premature operation of the trip relays.

Another object -of this invention is to provide a protective system of the character mentioned in which the trip relays may be very rapid and their operation is instantaneous with completion of the operation of the power directional relays and the overcurrent relays.

A further object of the invention is to provide a protective system of the character mentioned embodying a control element or time equalizing means for preventing actuation of the trip relays until the directional relays, the overcurrent relays and the parts associated therewith have completed their operations, whereupon the trip relays are energized so that their actuation may be instantaneous.

The various objects and features of my invention will be fully understood from the following detailed description of typical preferred forms and applications of the invention, throughout which description reference is made to the accompanying drawings, in which:

Fig. l is a diagrammatic View of a portion of the electrical distribution system illustrating a power supply station feeding a loop which includes a plurality of line sections connected by sub-stations. Fig. 2 is an enlarged detailed diagrammatic View of one of the units provided by the present invention of the character that is provided at each end of each line. Fig. 2a is an across the wire diagram of the A. C. circuits shown in Fig. 2. Fig. 2b is an across the wire diagram ofthe D. C. circuits shown in Fig. 2. Fig. 3 is a diagrammatic view similar to Fig. 2 illustrating another form of unit of the invention and Fig. 4 is a diagrammatic View similar to Fig. 2 illustrating still another form of unit of the invention.

The typical loop system illustrated in the drawings includes a main station or power station A, a plurality of sub-stations C, D, E and F connected with the supply station A and with one another by lines G, I-I, I, J and K. The said lines and sub-stations are connected in series and with the main supply station A to constitute a complex system of the loop type.

The protective system of the present invention is associated with the distributing system illustrated in Fig l so that it is operable to cut out a line section in which a fault occurs without disturbing the other line sections of the system. The circuit illustrated is a three phase circuit and each of the lines G, H, I, J and K includes three conductors I0, I! and I2. The main conductors IU, II and I2 of each line extend to and connect with the bus bars I3, I4 and I5 of the stations connected by the lines. The present invention provides a unit X at each end of each line section, the units X being related or interconnected to selectively disconnect a faulted line section whether the fault thereon be a phase to phase fault or a phase to ground fault. A unit X is connected at each end of each of the line sections connecting adjacent stations, whether the stations both be sub-stations or a sub-station and a main station.

The several units X may be identical and I will proceed with a detailed description of one unit X, -it being understood that this description is applicable to the other units. The form of unit X illustra-ted in Fig. 2 of the drawings includes the combination of elements I will now describe in detail. The unit X illustrated in Fig. 2

includes a suitable circuit breaker I6 in the main lines Ii), ll and l2, ahead of the connection of said lines with the bus bars i3, Iii and I5. A source of current independent of the distribution system and carried by lines Il and i8 is employed to operate the circuit breaker i6. The lines Il and i8 are connected with power lines ISI and I32, respectively. The line Il may be directly connected with the power line I 3l while the line 8 is indirectly connected with the power line E32, as will be hereinafter described. The circuit for operating the breaker i5 includes a combination of relays which control said circuit and which are governed by the other elements of the unit X. The means for controlling the circuit breaker l5 includes three trip relays or overcurrent phase relays i9, 25 and 2l and a ground relay 3l connected in the breaker operating circuit so that closing of any one of them completes the circuit and effects operation of the breaker The trip relays. i9, 2G and 2l include normally open movable contacts Ia, 25a and 2da, respectively.

Transformers 23 and 2li are associated with the bus bars I3, Eli and i5 and the conductors Eil, il and I2, respectively, to be energized by the main power circuit. The transformer is a potential transformer and the transformer 2liis a current transformer. The unit X includes a directional relay 25 responsive to the direction of three phase power flow and connected with the transformers and with overcurrent relays 25, 21 and 28. A transmitting relay 29 is` under the control of the directional relay 25 or any one of relays 26, 2'! or 25 to start the operation` of a signal transmitter T and to govern a lockout relay 35. The transmitter T is controlled through contacts 95 and 97 vof' relay 25 and the coil of the relay 30 is controlled through contacts 9B and 99 ci the relay 29. The contacts of the lockout relay 35 are normally closed to cut out the trip relays I9, 25 and 2! by short circuiting the winding of relay i9 through contacts i5@ and i5?, by short circuiting relay 25 through contacts m6 and Iii?, by short circuiting the winding of relay 2l through contacts H35 and I2?, and hold open the circuit of one of the windings of the ground trip relay 3i at contacts l 29 and 255 to normally take the trip relays out of service.

The potential transformer 23 embodies primary windings 32 and 33 connected with the bus bars I3, Ill and I5 and secondary windings 32a and 33e energized by the windings 32 33, respectively. The secondary windings 32a and 33a are electrically connected with the directional relay 25 by connections 59, lil and 5I, the connection di! Vbeing grounded.

The above mentioned current transformer 2:2 ernbodies` secondary windings 25e, 25h and 24C associated with the main power lines iti, il and l2, respectively. One pole of each winding 25e, Zlib and 25C is connected with a common line 52 which extends to the relay 3i to be hereinafter described. Lines t3, lill and i5 are connected with the other poles of the windings 25e, 25h and 24C, respectively and extend to the current coils of the relay 25, as will be hereinafter described.

The directional relay 25 embodies a rotatable shaft or unit 56 carrying discs i? and i8 and a contact 59. The contact 59 is operable to engage a stationary contact 5I connected by a line 52 with a terminal 52a of the group of relays 26, 2l and 28. A line or conductor 55 connects the contact i9 with a line HSI which .in turn is connected with one pole of the winding of relay 29. A xed field element 53 is related to the disc l to suitably damp rotation of the unit 56 and the direction of torque on the unit 55 is controlled by windings 5i and 55 suitably associated with the disc il and windings 55 and 5l, and 58 and 59, related to the disc 58. The windings 54, 55 and 53 are energized by current from the transformer 2li and windings 55, 5l and 59 are energized by current from the transformer 23, As illustrated in Fig. 2, one pole of the winding 55 is connected with the transformer winding 25a by a connection 55 while the other pole of the winding 55 is connected with one terminal of the winding 'I3 of the relay 26 by a connection 5E. The winding 55 has one pole connected with transformer 23 by a line 55 and has its. other Y pole connected by a common connection 39a with a pole of winding 55 and a pole ci winding 5l. One pole of the winding 55 is connected with the transformer winding 2M by a connection '35 and the other pole of the winding 55 is connected with a terminal of the winding 5i of the relay 23 byV a connection 63. One pole of the directional winding 58 is connected with the transformer winding 2th by a connection lli and the other pole of the winding 58 is connected by a connection 65 with one pole of the winding l5 of relay 2l. The winding 5S has one pole connected with the potential transformer 23 by a connection and has its other pole connected with a pole of the winding 55 and a pole of the winding 5l by a common connection 39a. The other pole of the winding 5l is connected Withthe transformer 23 by a line 4 I The relay 26 is an overcurrent relay comprising stationary contacts it?, 'il and 255, and a movable contact l2 governed by a Winding 73. The stationary contact l5 is connected with a terminal 52a which in turn is connected with contact 5l of the relay 25 by a connection 52. Thev contact II is connected with terminal El which in turn is connected by line 82 with the power line G32. A conductor or line lil connects one pole of the relay winding 'F3 with terminal i535 of the relay 3Q and the line 6E] connects with the other pole of the winding '53. The terminal Illl is, electrically connected with a pole of the winding |91 of relay I 9 by a line l5. Contact 25S of relay 26 is connected with one pole of a winding 25I of the relay 252 by a connection 253. The other pole of winding 25S is connected with the power line I3! by a connection 254,

The relay 2l is an overcurrent relay including three stationary contacts l, ll and 255, a movable contact 78 and winding 'i9 controlled by the movable contact 'I8'. The stationary contact I5 is connected with terminal 52a and stationary contact 'il is connected with terminal 8I. Winding 'I9 of relay 2l has one pole connected with the line 54 exten-ding from the relay 25 and has its second pole connectedwith the terminal Iil of relay 30 by a connection 35. The terminal |05 is connected with a terminal of the winding 2!)b of relay 25 by a conductor or line 85a. -Contact 255 of relay 2l is connected with line 253 which in turn is connected with the winding 25I of relay 252.

VThe relay 28 is an overcurrent relay embodying stationary contacts 88, 89 and 255, a movable contact and the winding 9! operating the contact 90. Stationary contact 88 is connected with the above described terminal 52a and stationary contact 89 is connected with the above described terminal SI. One pole of the winding 9| of relay 23 is connected with the winding 56 of the relay 25 75 by a connection 63 and a line 94 connects the other pole of the winding 9| with terminal |05 of relay 30. A line 95 connects the terminal |05 with one terminal of the winding 2 b of relay 2|. Stationary contact 256 of relay 28 is connected with line I253 which in turn is connected with the winding 25| of relay 252 as described above.

The transmitting relay 29 embodies four stationary contacts 95, 91, 98 and 99, a movable contact and a winding 84 for operating the movable contact |08. Connections |0| and |02 connect the stationary contacts 95 and 91, respectively, with the signal transmitter T whereby the transmitter is energized upon actuation oi the contact |00. Contact 98 is connected with the power line |32 by a connection 99h. Contact 98 is connected with winding |08 of relay 30 by line 99a and a connection 251 connects the other pcie of the winding |08 with line |1 which in turn is connected with power line |3| for completing the circuit between the winding |08 of the relay 30 and the power line 32 when contact |00 is actuated. Winding 84 of relay 29 has one pole connected with line |3| by a connection 251a and line 9| connects with the other pole of winding 84.

The lock out relay 30 for controlling or locking out the trip relays I0, 20 and 2| includes the stationary contacts |54., |05, |08 and |91 referred to above, stationary contacts |29 and 204, and a movable contact |01a controlled by winding |08. The winding |08 is normally energized under the control of the relay 252 to hold the movable contact |01 against the contacts |04, |05, |00 and |01 and out of engagement with contacts |29 and 204. One pole of the winding is connected with contact 99 of relay 29 by line 80a as described above, and is also connected with a receiver R by a line |083. The other pole of winding |08 of relay 30 is connected with line l1 as described above.

The protective unit X illustrated in Fig. 2 includes means that is primarily responsive to phase to ground fault conditions. This means includes, generally, a ground transformer |28, the relay 3| mentioned above, and a ground overcurrent relay |2|.

The ground overcurrent relay |2| includes three stationary contacts |22, |24 and 258, a movable contact or element |25 for cooperating with the stationary contacts and a coil |28 for controlling the movable element |25. The stationary contact |22 is connected by a conductor |28 with the contact |29 of relay 30 and is connected with the movable contact |20 of relay 9| by line |33. Contact |24 is connected with the terminal 8|. The winding |25 has one pole connected by a line |35 with a pole of the transformer winding |31 energized from the transformer |20. The second pole of the winding |25 is connected with the terminal |35 of relay 3! by a line |38. The stationary contact 258 of relay I2! is connected with line which in turn is connected with the winding 25| of the relay 252,

The transformer |25 is connected or associated with the bus bars i8, |4 and i5 and may include three primary windings |159. Each winding |20 has a pole connected with a bus bar and a pole connected with a common ground line IM. The transformer |25 further includes secondary windings |42 connected in series and in a circuit carried by line |42 which energizes the above nienfrom one phase of the power circuit to ground and is associated with the current transformer 24 to detect the direction of such a fault. The directional relay 3| includes a movable shaft or element |50 carrying the above mentioned contact |39 and a disc |5| secured to the element |50. A xed eld element |52 is related to the disc |5| to damp rotation of the element |50. Windings |53 and |54 are suitably related to the disc |5| to effect rotation of the disc and element. Winding |53 has a pole connected with the winding of the current transformer 24 by a connection 42. The second pole of the winding |53 is connected by a line |55 with the terminal |01 of relay 30. A line |51 connects the line |55 with one terminal of the winding 29b of relay 28. The windings of the trip relays |9, 29 and 2| have a com,- nion connection |50. Aline connects one pole of the winding |54 with one pole of the winding |02 to be hereinafter described. The other pole of winding |54 is connected with the terminal |39 of relay 3| by a connection |03. The movable contact |30 of relay 3| is adapted to turn in one direction to cooperate with the contact |85 and is adapted to turn in the other direction to cooperate with the contact |55. The stationary contact |55 is connected with the terminal |91 of relay 8| which in turn is connected with line |90. Line |90 is connected with line |9| which in turn is connected with one terminal of the winding 34. oi the relay 29 and with line 50 of relay 25. The other stationary contact |65 of the relay 3| is connected with one terminal or" a winding |09 by a line |98. The movable contact |30 is electrically connected with the stationary contact |29 of relay 30 by a connection |33.

The relay 3| includes a second movable element |80 carrying a contact |8| and a disc |82. Rotation of the disc |82 and the element |80 is damped by a fixed eld element |83 suitably related to the disc. The movable contact |8| of the relay 3i is connected with the contacts |92 and 2|C of the relays |9, 20 and 2| by a line |82. The relay 3| further includes a stationary contact |08 engageable by the movable contact |8|. The stationary contact |89 is connected with a contact 25| of the relay 252 by aline 200. A shunt line 252 connects the line 200 with the line 991 which in turn is connected with the power line |32 for operating the breaker i5 and with contact 88 of relay 29 and with the receiver R.. Line 283 extends from the power line |32 to the terminal |34 of the receiver R. The connection or line |08a is connected with the other terminal of the receiver. Rotation of the disc |82 is eiected by the relationship of the windings |09 and |02 which produces energization of winding 259, the winding 200 being operable to turn the disc. The winding |52 has a pole connected with the transformer winding |31 by a line and has its second pole connected by line |B| with the winding |54 described above. The winding |59 has a pole connected with the contact |65 by a connection |00 and has its second pole connected with a pole of the winding 280. The other pole of the winding 290 is connected with the contact 204 of relay 39 by a. line 203.

The relay 252 governs the relay 39, that is, under certain fault conditions the relay 252 deenergizes the relay 30 to allow the trip relays |9, 20 and 2| to function. The relay 252 includes two stationary contacts, the contact 28| and a contact 215. Contact 28| is connected with line 26|) and with shunt line 262, as described above. Stationary contact 215 is connected with the contact 99 of relay 29 by a connection 215. Relay 252 further includes a movable contact 211 coop-V erable with the contacts 25| and 215 and controlled by the winding 25|. Winding 25| of the relay 252 is normally de-energized, one pole of the winding being connected with the contacts 250, 255, 256 and 258 of the relays 26, 21, 28 and |2|, respectively, by the line 253, and its other pole is connected with the power line |3| by the connection 254. 'Ihe movable contact 211 normally cooperates with the contacts 26| and 215 so that a circuit is normally completed to the winding |09 of the lockout relay 3|). Energization of the winding 25| of relay 252 thus operates to cle-energize the lockout relay 5G to allow the trip relays I9, 20 and 2| to function. It will be observed that relay 252 prevents or delays de-energization of the lockout relay until the relays 25, 21, 28 or |2| have functioned to select or set up an energizing circuit for the proper trip relays I9, 29 and 2|, whereupon the relay 252 is energized to eifect de-energization of the lockout relay 39. The lockout relay is not de-energized until the relay 25 or 3| and a relay 25, 21, 2B or |2| have completed their operations at which time relay 252 de-energizes the relay 39 to allow operation of a trip relay i9, 29, 2| or 3|. The trip relays |9, 20, 2| and 3| may, therefore, be instantaneous or very rapid relays. In other words, if the time required for the operation of relays 25 and 29 or the relays 3| and 29 is equal to the time required for the operation of a relay 28, 21, 28 or |2| and the relay 252, the trip relays |9, 20, 2| and 3| may be instantaneous.

Each of the above described units X includes a transmitter T and a receiver R whereby an interconnection is established between the two units X at the ends of each line section. The interconnection between the units may be of any suitable character, for example, it may be a wired connection or may be a wired radio connection carried by the line being protected.

The transmitter T and the receiver R of a given unit X have one pole connected to ground through a ground connection 215 and have their other pole connected with one of the power lines, say the line through a connection 21| having a coupling capacitor 212 and the line may be provided with a radio frequency trap 213 between the line 21| and the busses |3, I4 and |5. The transmitters T and receivers R of the units X at the opposite ends of each line section are connected for cooperation with one another andare isolated from the transmitters and receivers of the other units X whereby a signal sent by one unit of a line section only operates the receiver R at the opposite end of that section.

The relays 25 of all of the units X in the system are of the type known in the art as power directional relays. The relays 25 of the several units X are such that when the direction of power current flow is toward the bus of a unit X the torque on the discs 41 and i8 of its relay 25 causes its contacts 49 and 5| to be in a closed condition. When the power current flow is away from the bus of a unit X the torque on the discs 41 and 28 of its relay 25 causes the contacts G9 and 5|v to be open. Referring to Fig. 1 of the drawings the normal flow of power is from the station A to the sub-station C, over the line section G so that the power ow at the unit X of the station A at the end of said section is away from its bus and the relay 25 of the unit has its contacts 49 and 5| open and the power flow at the unit X of the line section G located at the sub-station C is toward its bus so that the contacts oi the relay 25 of the unit X are closed. The relays 25 are responsive to normal load current flow but in the event of a short circuit condition the short circuit current is greater than the normal load current and the relay 25 is responsive to the short circuit. Thus the relays 25 are controlled by the short circuit current when a fault condition exists.

In the event that a phase to phase short circuit occurs in a line section, for example in the line section I between stations E and D on the lines |9 and the current transformers 22a and Zlib at each end of the said section are energized causing the units X at both ends 'of the section to function. The functioning of a unit X under such circumstances is as follows. The current transformer 2li is electrically connected with the operating windings of the relay 25 in the manner described above to eiect operation of the relay 25 to open its normally closed contacts 49 and 5| or to close its normally open contacts i9 and 5| depending upon whether the normal power current flow in the associated line section is toward or away from the bus of the unit X. The windings of relays 29, 21 and 28 are connected in series with the windings of the relay 25 by the connections described above so that certain of the relays 26, 21 and 28 are operated to condition or set up circuits for energizing their related trip relays i9, 29 and 2|. Energization of a relay 25, 21 or 28 also eifects energization of the relay 252 which in turn de-energizes the lock-out relay 9G. It is to be understood that the lock-out relay 30 remains energized to prevent actuation of the trip relays I9, 29 and 2| until energization of the relay 252. When the lock-out relay 3G is deenergized by the above described action of the relay 252 the trip relay |9 and/or trip relay 20 and/or trip relay 2| operates. The relays I9, 20 and 2|v are associated with the energizing means of the circuit breaker |6 so that the breaker is tripped or operated when a relay |9, 2|) or 2| is energized. In practice a phase to phase fault in a line section results in the energization of one or more of the relays |9, 2|! or 2| through the relays 25, 2B, 21 and/or 28 and under the coordinating control of the relays 252 and 30 due to the fact that the contact 49 of relay 25 is not in engagement with contact 5|.

When a phase to phase short occurs in a line section external to the line section of the system being protected by the units X under consideration, the direction of the current from the transfo-rmer 24 is reversed in the relays of the units X so that the contact 49 of the relay 25 of each unit X engages its related contact 5|. Such a phase to phase short circuit results in energization of one or more of the relays 26, 21 and 28 to close their contacts which in turn causes the terminals 52a and 8| of the relays to be electrically connected. Engagement of the contact i9 with the contact 5| completes the circuit to the relay 29 through the connections 55, 59|, |32, 251 and |3|, described above. The resultant energization of relay 29 engages contacts 95 and 91 which control the operation of the transmitter T. When the transmitter T is thus put into operation it sends a signal over the line to the receiver R at the other end of the line. The above described operation of relay 29 also prevents de-energization of the lock-out relay 39 by completing and maintaining an energizing circuit to the relay 30 through the closing of contacts 98 and 99. So long as the energization of the lockout relay 30 is maintained it cuts out the windings of relays I9, 20 and 2| and thus prevents the system from operating to trip the breaker.

When a phase to phase fault occurs on a line of the system the units X at the ends of that line operate so that their breakers I6 open. On the other hand, when a fault occurs in a line as a result of a fault on another line of the system the unit X receiving such current flow cuts out or becomes locked so that its breaker cannot function and sends a signal which is carried by its line to the unit X at the other end of said line, which signal effects the locking out of the last mentioned unit X so that its breaker I6 does not function.

The magnitude of current flow resulting from a phase to ground fault on a line is not ordinarily sufficient to operate the relays 25, 26, 21, 28, 19, 20 and 2|, as described above, but may be suincient when aided by the cu rent from the ground transformer |20 to operate the directional element |50 of the relay 3|. A phase to ground fault results in current flow in the relay 3| of the unit X at the end of the line to close the contacts |30 and |66 to effect energization of the winding 200 of the relay 3|. Winding 200 is energized through induction from the winding |62 to winding |69. This energization of Winding 200 results in closing of the contacts |8| and |89 to complete a circuit through the connections |32, 99h, 262, 260, |84, I8, |1 and |3| to trip the breaker I6.

In the event of a phase to ground fault on the bus side of the unit X relay 3| operates as just described except that current flow in the winding |53 is reversed to move contact |30 into engagement with contact |65. Relay |2| is energized from transformer |31 through line 20|, winding |62, line |6|, winding |54, line |63, line |38 and line |35. Closing of contact |30 with contact |65 completes the circuit to the relay 29 through contacts |22 and |24 of energized relay |2|. Contacts 96 and 91 of relay 29 close to complete the circuit to the transmitter T which sends a signal to the unit X at the other end of the line section to lock it out as above described. Under the fault condition just mentioned contact |30 of relay 3| is out of engagement with contact |66 so that winding 200 is not energized and contacts |8| and |89 of relay 3| do not close and the breaker I6 cannot trip,

'I'he circuit connections will now be more specifically traced under typical fault conditions.

Phase to phase internal fault in a [me section When a phase to phase short circuit occurs in a line section, for example, in the line section I between the sub-stations E and D and on the lines and |I the current transformers 24a and 241D at each end of said section are energized. The operation of a unit X under such circumstances is as follows. The current transformer 24a of the unit X is.` energized by the fault current in line |0 and the transformer 24b is energized by fault current in the line Il, the current flow in the transformers being in opposite directions. The secondary current of the transformer 24a is carried by the conductor 43 to the coil 54 of relay 25 and from relay 25 to the coil 13 of relay 26 by conductor 60v and from the relay 26 to the contact |04 of relay 30 by conductor 14. Since relay 30 is normally energized the current flows from contact |04 to contact |06 and thence by line 85 to coil 19 of relay 21, from relay 21 by line 64 to the coil 58 of relay 25 and then from relay 25 by line 44 to the current transformer 24h, the circuit being completed by the tie between the transformers 24b and 24e. The current flow through the coil 13 of relay 25 causes contacts 10, 250 and 1| to be made and current in the coil 19 of relay 21 causes contacts 16, 255 and 11 to be made. Current ows from power line |32 through line 82 to the contact 255 and from contact 1| to contact 250 and then by line 253 to the coil 25| of relay 252 and then from the relay 252 to the power line |3| by the conductor 254, thus completing the circuit and actuating ,the relay 252. Actuation of relay 252 causes contacts 25| and 215 to open, breaking the circuit to the coil of relay 30 which was normally established from power line |32 through line 99h, contacts 26| and 215, lines 216 and 99a, coil |63 of relay 30 and the line 251 to the power line 13|. De-energization of relay 35 allows the current carried by line 14 to contact |04 to pass through the line 15 to coil |9b of the trip relay |9, from relay I9 by line 165 to coil 20b of trip relay 20 and from relay 20 by line 85a to contact |06 of relay 30 and from relay 30 by line 85 as previously described. Energization of relay I9 closes contacts |9a and lilc and energization of relay 20 causes contacts 20a and 20C to close. This completes the circuit from the power line |32 through these contacts to the line |84, through line I8 to the trip coil of the circuit breaker I5 and from the circuit breaker coil by line |1 back to the power line |3| to complete the breaker circuit. The units X at the opposite ends of the line section I having operated as just described clear the faulted line section I.

Phase to ground fault internal of a Zine section In the event of an internal ground fault from the line I0 to the ground in line section I the units X at the opposite ends of the section operate in the sarne manner and as follows. Fault current in line i0 energizes current transformer 24a and current from the transformer flows over line 43 through coil 54 of relay 25, from relay 25 over line 60 through coil 13 of relay 26, from relay 26 through line 14 to the Contact |04 of relay 30 and to contact |01, and from relay 30 by line |56 to coil |53 of relay 3|, and from relay 3| by line 42 to the transformer 24a, completing the circuit. The ground fault current returning from the power line |0, is carried by line |4| of the ground bank |40, causing current to flow in the circuit of line |44 and through the transformers secondary |42, thus energizing the current transformer |31. Current ows from the secondary of transformer |31 by line |35, through coil |26 of relay |2|, and from relay |2| by line |38 to coil |54 and coil |62 of relay 3|, and from relay 3| by line 20| to the secondary of transformer |31 to complete the circuit. The torque on the disc |5l produced by the energized coils |53 and |54 causes the contacts |30 and |66 to close. Current in the coil |20 of relay |2| closes contacts |24, 258 and |22. Power from line |32 flows through line 82 and contacts |24 and 258 of relay |2|, through line 253 to coil 25| of the relay 252, then through line 254, back to power line |3| to complete the circuit. Actuation of relay 252 opens contacts 26| and 215 to break the energizing circuit of the relay 30. Deenergization of relay 30 closes contacts |29 and 204. Coil |62 of relay 3| energized by the circuit just described causes coil |69 to be .energized by induction so that current flows from the coil |69 over line |68 through closed contacts |66 and |30, over line |33 through closed contacts |29 and 294 through line 293 through coil 200 and the tie between coil 290 and coil |59 to complete the circuit. Torque produced by the coils 200 and |62 causes the disc |82 to turn and closes the contacts |8| and |89. Current from line |32 carried by lines 99band 250, closed contacts |89 and |8| of relay 3| flows from relay 3| through lines |84 and |8 to the coil of the breaker I6, and then passes by line |1 to the power line |3| to complete the breaker circuit. Tripping of the circuit breakers I6 of the units X at the ends of the affected line section I clears the line section.

Phase to ground fault etemal of a Zine section In the event of a phase to ground fault external of a line section, say the section J, `the operation of the protective unitJ X at the station E on the line section I is as follows. Under this condition the current transformer 24a of the said unit X is energized by current ow in a direction opposite to the direction of flow when there is a phase to ground fault external of the section. The secondary current from the transformer 2lia ows on line 42 to coil |53 of relay 3| and from relay 3| over line |55 to contact |51, thence to contact |94 of energized relay 39, then over line 14 to coil 13 of relay 26, from relay 26 over line to the coil 54 of relay 25, and then from relay 2 5 over line 43V to the current transformer 2&1a to complete the circuit. The ground fault current returning from line l0 is carried by line |4| of the ground bank |40, causing current to flow through line |44, through the secondary |42 of the transformer |40, thus energizing the current transformer |31. Current ows from the secondary of transformer |31, by line |35 through coil |26 of relay |2| and thence by line |38 to the coil |54 and the coil |52 of relay 3| and then by line 20| to the secondary of transformer |31, completing the circuit. Torque produced by the coils |53 and |54- on the disc |5| causes the disc to turn to close contacts |30 and |65. Current in the coil |26 of relay |2| brings about the closing of contacts |24, 258 and |22. Power from line |32 ows through line 82, closed contacts |24 and |22 of relay |2|, through line |28, through closed contacts |39 and |65 of relay |3|, through lines and |9| to the coil 83 of relay 29 and then through line 251a to the power line |3| to complete the circuit and energizing relay 29. Energization of relay 29 closes contacts 98 and 99 and 96 and 91. Current flows from line |32 through line 82 to closed contacts |24 and 258 of relay |2|, then through line 253 to the coil 25| of relay 252 and from the relay 252 to the power line |3| through line 254, completing the circuit. This operates relay 252 so that its contacts 29| and 215 are opened, but does not effect the cie-energization of relay 39 because a circuit remains completed through line |32 and line 99D to closed contacts 98 and 99 of relay |29, from relay |29 by line 99a to the coil |08 of relay 30 and from relay 39 to the power line |3| by way of line 251. When relay 30 remains energized the contacts |29 and 204 are open so that the circuit through coils 299 and |59 at the disc |32 of relay 3| remain de-energized. lIhus the tripping means or tripping part of relay 3| does not operate to cause tripping of the breaker I6. Energization of relay 29 as just described completes a circuit to the transmitter T,- through lines |9| and |02 and contacts 496 and 91. The transmitter T sends a signal through condenser 212, line ,21| and line of the section I to the line 21| at the unit X at the sub-station D, and through the condenser 212 to the receiver R of the unit X at the sub-station D. This signal closes switch or contact |34 of the receiver R of the unit X Y just mentioned. The current from power line |32 flows through line 263 tothe contacts |34, then over line |08'EL to the coil |08 of relay 30, and from relay 30 over the line 251 to the power line |3| to complete the circuit through the lock-out relay 30. This energization of the lock-out relay 30 prevents actuation of the trip relays i9 and 29 so that the breaker I6 of the unit X at the substation D is not tripped. Thus the circuit breaker I6 of the units X at the opposite ends of the section I are prevented from operating when a phase to ground fault occurs on the line section J.

Phase to phase fault external of a. Zine section Referring again to Fig. l and considering the operation of the protective units at the ends of the line section I when there is a short circuit on the lines l0 and |I of the line section J the operation of the unit X at the station E on the line section I is as follows. Under a condition of this character current flow in the lines I0 and of the unit X at the station E on the section I energizes the current transformers 24a and 24b to cause current to flow from the transformer 24h on the line 44, through coil 58 of relay 25, from relay 25 through line 55 to the coil 19 of relay 21, and from relay 21 by line 85 to the contact |96 of relay 30 and from Contact |05 to contact |04, then by line 14 to coil 13 of relay 26 and from relay 26 by line 69 to coil 54 of relay 25 and from relay 25 by line 43 to current transformer 25a, the tie between the transformers 24a and 24b completing the circuit. The torque produced by energized coils 54 and 55 on disc 41 of relay 25 and the torque produced by energized coils 58 and 59 on disc 48 of relay 25 closes contacts 49 and 5|. The current in coil 13 of relay 26 actuates the relay to close con- A tacts 10, 250 and 1|, and current in the coil 19.

of relay 21 actuates the relay to close the contacts 16, 255 and 11. From power line |32 current flows through line 9 2 to contacts 11 and 1|,

from contacts 16 and 10 through line 52 to closed |3|, completing the circuit. Energized relay 252 opens contacts 29| and 215, but as relay 29 is operative at this time the circuit to the coil of relay 30 remains closed from power line |32 through line 99h, contact 98 of relay 29, contact 99, line 99a, and the coil |08 of relay 39 and from the coil 30 by line 251 to the power line |3| As the relay 30 prevents current flow to the trip relays |9 and 20, these relays remain inactive and the breaker |6 is not tripped. Energization of relay 29 completes a circuit to the transmitter T through lines I0| and |02 by the contacts 96 and 91. Transmitter T sends a signal through condenser 212 and line 21|, over power line of the section I tothe. line 21| and condenser 212. of

the unit X at the sub-station D, delivering a signal to the receiver R. This signal closes contact |34 of the unit X at sub-station D. This causes current to flow through line 263 from power line |32 and through contacts |34 and over the line |08EL to the coil |08 of relay 30. The current continues from relay 30 through line 251 to the power line |3| to complete the circuit through the relay 30. This energization of relay 30 prevents actuation of the trip relays I9 and 20 sothat the breaker I6 of the unit X at the substation D is not tripped. Thus the breakers I6 of the units X at both ends of the section U are prevented from being tripped by a phase to phase fault condition external of the line section.

Fig. 3 of the drawings illustrates a form of unit X adapted to be employed in the protective system in the same manner as the above described unit X. The unit X illustrated in Fig. 3 is similar to the type of protective unit described in the above-mentioned Patent No. 1,940,303, differing therefrom in that it includes means for so co-ordinating the operations of the various elements that the trip relays may be very rapid or instantaneous relays. The unit X is similar to the unit X described above, differing therefrom in that it embodies a trip relay 9 replacing the above-described trip relay elements oi the relay 3|.

The ground directional relay 3| of the unit X embodies the rotatable element |50 carrying the disc I5| and the contact |30. The contact |30 is adapted to engage the contact |65. The iiXed eld element |52 dampens rotation of the disc |5I and the element |50. The windings |53 and |54 of the relay 3| are related to the disc |51 to eiect rotation of the disc and the element |50. Line 42 connects one pole of the winding |53 with the current transformer 24. The other pole of winding |53 is connected with one pole of the winding |26 of relay |2I by a line 309. A line 3I0 connects one pole of the winding |54 with the transformer winding |31 and a line 3H connects the other pole of the winding |54 with the other pole of winding |31. The stationary contact |65 of relay 3| is connected in line I9! by a line 300. Line |33 connects the movable contact |30 with the stationary contact |22 of relay |2|. It will be noted that contacts |29 and 264 of relay 30 are eliminated in the unit X.

Trip relay 9 is operable under certain ground fault conditions to trip the circuit breaker |6. Relay 9 includes two stationary contacts 30| and 302. A line 303 connects contact 30| with the common line |50 of the trip relays I9, 20 and 2|. Line 304 connects the stationary contact 302 with line |84. The trip relay 9 further includes a movable contact 305 operated by a coil 306. Common line I 60 is connected with one pole of the relay coil 306. A line 301 connects the other pole of winding 30B with the contact |01 of the lock-out relay 30. A line 308 connects one terminal of the winding |26 of relay |21 with the contact |01 and, therefore, with line 301 extending to the Winding 306 of relay 9. The unit X illustrated in Fig. 3 is otherwise identical with the above-described unit X and the corresponding reference numerals are employed on corresponding elements of the two units.

The action or operation of the unit X in the case of a phase to phase fault is the same as that of the above-described unit X. In the event of a phase to ground fault in the line section protected by the unit X the relay 25 is energized to close its contacts 49 and 5| but the magnitude of the current delivered to the coils of relays 26, 21 and 28 may be insuicient to operate the relays. Under the phase to ground fault conditions just referred to Where the ground fault current is flowing toward the unit X' from an adjacent line section, current flow in the Winding |53 of relay 3| moves the contact |30 into engagement with contact |65. This energizes the winding 8'4 of relay 29 through lines 300, |9I and 251e. send a signal to the unit X at the adjacent line section to hold it in service. Simultaneous with the energization of relay 3| winding |26 of relay 12| is energized through line 309 to close contacts |25 and 258. This completes the energizing circuit to coil 25| of relay 252 through line 253. Energization of relay 252 breaks the circuit to the coil |08 of lock-out relay 30. Thus trip relay 9 is allowed or conditioned to operate by current received through lines 301 and 308. The relay 9 completes a circuit to operate the breaker I6 as will be readily understood. It will be noted that relay 252 normally conditions the lock-out relay 30 and that energization of r-elay 252 immediately following operation of relay I2I de-energizes the relay 30 so that the trip relay 9 may be very rapid or instantaneous. Trip relay 9 is not conditioned until relay |2| has cornpleted its operation, the relay 252 serving to sustain relay 30 until relay |2| is fully operated. Thus the provision of the relay 252. allows the trip relay 9, as well as the trip relays |9, 20 and 2 I, to be very rapid or instantaneous relays.

Fig. 4 of the drawings illustrates a protective unit X2 similar to the above-described unit X and diiering therefrom in that it embodies balanced current trip relays I9', 20', 2| so related that the unit is not responsive to balanced three phase faults or balanced over-current conditions resulting from out of step conditions in the system but will properly select and clear the line section involved in any other type of fault. Corresponding reference numerals are applied to corresponding elements in Figs. 2, 3 and 4.

The trip relay I9 includes the operating coil |99, the trip relay 20 includes the operating coil 20b andl the trip relay 2| includes the operating coil 2lb all of which are connected and energized in the same manner as in the abovedescribed protective units X and X". The trip relay I9' further includes a balancing coil or restraining coil |96. Coil |9e is connected in the relay system so that under normal operation, current from another phase flows through it so that the phase relation of the current in the coils |9e and I9b is 120 apart in a Y relationship, so that the coil 9e is operable to restrain or prevent closing of the contact |99. The restraining coil I9e is interposed in line 350 which connects one pole of the winding 19 with the contact |06 of the lock-out relay 30. The contact |06 is connected with the operating coil 20b of trip relay 20 by line 85a. The restraining coil I9b is thus energized simultaneously with the operating coil 20b of trip relay 2|. The coil 20b is associated with the overcurrent relay 28. Restraining coil 20e of trip relay 20 is interposed in a line 35| which connects one pole of the winding 9| with the contact |05 of relay 30. Line 95 connects said contact |05 with one pole of the operating winding 2|b of relay 2|. Current flowing through the restraining coil 20e is from a different phase than current in the operating coil 20h. The phase relationship of current in the two coils 120 apart in a Y formation is such Relay 29 energizes the transmitter T to y that the coil 2&9 is operable to restrain or prevent operation of the Contact 2tEL When both coils are energized. The restraining coil Ele of relay 2l is interposed in line 352 which connects one pole of the Winding i3 of relay 2@ with t'ne Contact IEM of relay 3B. The line l5 connects contact li with one pole of the operating coil i910 of relay i9. The current sup-plied to the coils Ib and 2lc is from different phases 120'apart in a Y relationship. Y

The operation of the unit X2 illustrated-in Fig. 4 is substantially the same as that of the above described unit X except that the unit X2 is not responsive to a balanced three phase fault and is not affected by or responsive to an out of step condition in the system resulting in a reactance center in the line section protected by the unit, The unit X2 is intended primarily for use in a protective system for protecting a distribution system having two or more synchronous generators or synchronous machines and may be employed in a system of the character described in Patent No. 1,965,896. The unit X2 embodying the above-described restraining coils ge, 20e and 21e of the trip relays i9', 2li' and 2l', respectively, is not responsive to or sensitive toI line instability of a reactance center resulting from an out of step condition, but is responsive to every other kind of fault condition except balanced threephase faults which are very rare. The unit X2 operates under a phase to ground fault in the same manner as the unit X'. In the event of a phase to phase fault, current from one phase or line lll, Il or l2 flows through the operating coil I9b, 2gb or 2lb of a trip relay i9', 2li or 2l after passage through the coil of a relay 26, 2'! or 28, to close or operate the contact lSa, 29a or 2l2L of the related trip relay. vThe contacts 59a, 29a and 2 la of the trip relays are normally open and the above-described current now through the energized coil ISD, 20h or 2lb is such that the torque is opposite to that in the restraining coils E9e, 20e and 2ie. When an operating coil 19h, Zob or 2lb is energized by an overcurrent, as just described, the restraining coil 19e, 2E@ or Zie of another relay i9', 2Q or 2i' is simultaneously energized. It is to be understood that the trip relays i9', 2B and 2l', as Well as the trip relay 9, are under the control of the lock-out relay 36 which in turn is under the control of the relay 252. Relay 252 prevents de-energization of the lock-out relay 3B and so long as relay 3G remains energized it short circuits the operating coils of the trip relays i8', 2d and 2l to normally prevent their operation. The operation or energization of the relay 252 follows the operation of the relays 26, 2l and/or 28 so that the lock-out relay 3B is not fie-energized until completion of the operation of the relays 25, 21 and/or 28. Accordingly, the trip relays i9', 2Q and 2l and the relay Q may be instantaneous with the de-energization of the lock-out relay 3a and the trip relays may be very rapid or instantaneous relays.

I-Iaving described only typical preferred forms and applications of my invention, I do not wish to be limited or restricted to the details herein set forth, but Wish to reserve to myself any variations or modications that may appear to those skilled in the art or fall Within the scope of the following claims.

Having described my invention, I claim:

l. In a protective system for a sectional electrical distribution system, a protective unit for one end of one line section of the system, comprising, a circuit breaker controlling said section, the circuit breaker having a trip coil, an energizing circuit for the trip coil of the breaker, a current transformer associated Withv said section, a trip relay controlling said circuit and operable to effect the energizaton of the trip coil of the circuit breaker and adapted to be operated by current from the current transformer, a lockout relay normally preventing actuation of the trip relay, an overload relay energized by current from the current transformer, and a control relay governed by the overload relay operable to condition the lock-out relay to permit operation of the trip relay following energization of the overload relay.

2. In a protective system for a sectional electrical distribution system, a protective unit for one end of one line section of the System, comprising, a circuit breaker controlling said section the circuit breaker having a trip coil, an energizing circuit for the trip coil of the breaker, a current transformer associated With said section, a trip relay controlling said circuit and operable to effect the energization of the trip coil of the breaker and adapted to be operated by current from the current transformer, a lock-out relay normally preventing actuation of the trip relay, an overload relay energized by current from the current transformer, a signal transmitter, a signal transmitting relay controlled by the overload relay to initiate operation of the signal transmitter, and a control relay governed by the overload relay operable to condition the lockout relay to permit operation of the trip relay following energization of the overloadrelay.

3. In a protective system for a sectional electrical distribution system, a protective unit for one end of one line section of the system, comprising, a circuit breaker controlling said section, the circuit breaker including a trip coil, an energizing circuit for the trip coil of the breaker, a current transformer associated with said section, a trip relay controlling said circuit and operable to effect the energization of the trip coil of the breaker and adapted to be operated by current from the current transformer, a lockout relay normally preventing actuation of the trip relay, a ground transformer connected with the line, an overload relay to be energized by current from the ground transformer, and a control relay governed by the overload relay and operable upon energization of the overload relay to condition the lock-out relay to permit operation of the trip relay following operation of the overload relay.

4..In a protective system for a sectional electrical distribution system, a protective unit for one end of one line section of the system, comprising, a circuit breaker controlling said section, the circuit breaker includinga tripY coil, an energizing circuit for the trip coil of the breaker, a current transformer associated with Vsaid section, a trip relay controlling said circuit and operable to effect the energization of the trip coil of the breaker and adapted to be operated by current from the current transformer, a ground transformer connected With said line section, a trip relay controlling said circuit operable to elect the energization of'the breaker and adapted to be operated by residual current from the line section upon residual current flow in a single direction in said section, a-lockout relay normally locking out the said trip relays, a phase overload relay to be energized by current from the current transformer, a ground overcurrent relay to be energized by said residual current, and a control relay governed by either of the said overload relays and operable to condition the lock-out relay to allow operation of a trip relay following operation of one or both of said overload relays.

5. In a protective system for a sectional polyphase electrical system, a protective unit for one end of each section of the system comprising, a circuit breaker controlling said section of the line, the circuit breaker including a trip coil, an energizing circuit for the trip coil of the breaker, a current transformer associated with said section, balanced trip relays controlling said circuit and operable to effect energization of the trip coil of the breaker and operable by current from the transformer only when there is an unbalanced phase fault inthe said line section, a lock-out relay normally locking said trip relays, an overload relay energized by current from the transformer, and a control relay governed by the overload relay operable to condition the lockout relay to permit operation of the trip relays following operation of the overload relay.

6. A protective system for a sectional multiphase power line including, protective units at the ends of each section of the line, each unit including, a circuit breaker controlling the line section, the breaker including a trip coil, an energizing circuit for the trip coil, a plurality of trip Irelays controlling the said circuit and operable to eiect energization to the trip coil, means operatively connecting the phases of the line section and the trip relays to supply fault current to the trip relays to operate the Same, normally energized lock-out means preventing operation of the trip relays, and means associated. with the iirst mentioned means to de-energize the lock-out means.

7. A protective system for a sectional multiphase power line including, protective units at the ends of each section of the line, each unit including, a circuit breaker controlling the line section, the breaker including a trip coil, an energizing circuit for the trip coil of the breaker, a plurality of trip relays controlling the said circuit and operable to eiect energization of the trip coil, means operatively connecting the phases of the line section and the trip relays to supply fault current to the trip relays to operate the same, normally energized lock-out means preventing operation of the trip relays, and a control relay energized by the rst mentioned 2 means for de-energizing the lock-out relay.

LLOYD F. HUNT. 

